Add support for OVM_MAIN searchScope in isds_find_box_fulltext()
A specification change before 2015-11-09 added a new value to searchScope
element of ISDSSearch2 service. This service is implemented by
isds_find_box_fulltext() function and the searchScope is implemented as
isds_DbType enum.
Therefore this change adds a new DBTYPE_OVM_MAIN value to isds_DbType enum.
This value is recongized only by isds_find_box_fulltext(). Other functions
refuse it. This is the same case as DBTYPE_SYSTEM value.
The DBTYPE_OVM_MAIN allows to search for non-subsidiary OVM boxes by
a fulltext criteria.